Investigation of SiC Trench MOSFETs’ Reliability under Short-Circuit Conditions

In this paper, the short-circuit robustness of 1200 V silicon carbide (SiC) trench MOSFETs with different gate structures has been investigated. The MOSFETs exhibited different failure modes under different DC bus voltages. For double trench SiC MOSFETs, failure modes are gate failure at lower dc bus voltages and thermal runaway at higher dc bus voltages, while failure modes for asymmetric trench SiC MOSFETs are soft failure and thermal runaway, respectively. The shortcircuit withstanding time (SCWT) of the asymmetric trench MOSFET is higher than that of the double trench MOSFETs. The thermal and mechanical stresses inside the devices during the short-circuit tests have been simulated to probe into the failure mechanisms and reveal the impact of the device structures on the device reliability. Finally, post-failure analysis has been carried out to verify the root causes of the device failure.

Cochlear Implant Failure in the Pediatric Population

Background and Objectives: In cochlear implant (CI) surgery, the results and causes of revision and reimplantation may guide surgeons in establishing surgical protocols for revision surgery with safe audiological outcomes. The aim of this study was to review our experience in terms of etiology, surgical strategy, and hearing outcomes in pediatric patients who underwent CI removal and reimplantation.Subjects and Methods: All patients received implants of the same brand. Pre and postoperative Categories of Auditory Performance score and aided free-field pure tone audiometry thresholds were noted. In vivo integrity tests were performed for each patient and the results of ex vivo tests of each implant were obtained from manufacturer.Results: A total of 149 CIs were placed in 121 patients aged <18 years. The revision rate in children was 6.7% (10/121 children). Six patients had a history of head injury leading to a hard failure. The causes of reimplantation in others were soft failure (n=1), electrode migration (n=1), infection (n=1), and other (n=1). All patients showed better or similar postreimplantation audiological performance compared with pre-reimplantation results.Conclusions: It is very important to provide a safe school and home environment and educate the family for reducing reimplantation due to trauma. Especially for active children, psychiatric consultation should be continued postoperatively.

Reliability modeling for dependent competing failure processes with phase-type distribution considering changing degradation rate

In this paper, a system reliability model subject to Dependent Competing Failure Processes (DCFP) with phase-type (PH) distribution considering changing degradation rate is proposed. When the sum of continuous degradation and sudden degradation exceeds the soft failure threshold, soft failure occurs. The interarrival time between two successive shocks and total number of shocks before hard failure occurring follow the continuous PH distribution and discrete PH distribution, respectively. The hard failure reliability is calculated using the PH distribution survival function. Due to the shock on soft failure process, the degradation rate of soft failure will increase. When the number of shocks reaches a specific value, degradation rate changes. The hard failure is calculated by the extreme shock model, cumulative shock model, and run shock model, respectively. The closed-form reliability function is derived combining with the hard and soft failure reliability model. Finally, a Micro-Electro-Mechanical System (MEMS) demonstrates the effectiveness of the proposed model.

Reliability analysis for systems subject to mutually dependent degradation and shock processes

This paper studies the reliability problem for systems subject to two types of dependent competing failure processes, that is, soft failure and hard failure processes. A soft failure happens when the total degradation of the system exceeds a given critical level, while a hard failure occurs when the accumulative shock load caused by shocks surpasses the hard failure threshold. These two failure processes are mutually dependent due to the fact that external shocks will bring sudden increments in the degradation of the system, and the total amount of degradation will decrease the hard failure threshold of the system. The system fails whenever either of these two failure modes happens. Assuming that the arrival of shocks follows a Poisson process, the reliability function of the system under cumulative shock model is derived by using some analytical techniques. Some important reliability indices, including the mean lifetime of the system, the expected number of shocks until system failure, the probabilities of soft and hard failures, are calculated explicitly. Moreover, a special case that the hard failure process and soft failure process are mutually independent is also discussed. Monte Carlo method is employed to calculate the multiple integrals existing in the expressions of reliability function and reliability indices. A numerical example of the Reinforced Concrete pier columns on sea bridge is presented to illustrate the proposed model.

Reliability modeling and analysis for systems governed by multiple competing failures processes

Due to that the operating environment is becoming more and more complex and rigorous, the multiple competing failure modes for the reliability system is much commonly seen. In order to improve the system performance, a sensor-based degradation calibration policy (SBDC policy) is presented in this paper. The model considers the competing failure process which is described by the soft and hard failure modes. In detail, the soft failures occur when the degradation of the system exceeds the failure threshold, and the hard failures are caused by the same shock process. We use the Wiener process model to describe the soft failure and the shock process to describe the catastrophic failure. Meanwhile, in the shock process, the damage associated with the system is normal distributed which is related to the duration of the adjacent shocks. This extended model with calibrations has a good application value for the corresponding complex reliability systems which are subject to the dependent competing failure modes. By the model in this article, the system reliability and safety can be improved and the risk of the abrupt damage shall be reduced as the circumstance changes.

Back End of Line (BEOL) Pulse Nanoprobing Fault Isolation Technique on RF Device with Soft Failure Issue

The global radio frequency (RF) semiconductor market size is growing dramatically in recent years, especially with the growing demand for mobile devices, communication networks, automotive applications, etc. Failure analysis (FA) on RF devices is normally more complex than digital devices, especially when it involves soft failure. This paper discusses FA on an RF product soft failure issue by the pulsed currentvoltage (IV) nanoprobing technique. The device suffered from high-frequency failure and exhibited abnormal repetitive softstart signature. Previous publications on pulsed IV nanoprobing applications were mostly related to Front End Of Line (FEOL) issues and simulations. In most of these cases, the electrical abnormality could also be observed with normal DC IV measurement. In this paper, the pulsed IV nanoprobing was performed at the Back End Of Line (BEOL) interconnects to isolate the failure that was otherwise not detected with normal DC nanoprobing or the reported pulse IV measurement. The proposed method successfully isolate, simulate the failure, and helping us to identify the process and design rule weakness.